In the field of building services engineering, rail systems are used for securing conduits, for example, for water, heat, ventilation, air conditioning, and/or electrical installations, thereto, simply through the use of suitable fastening devices, such as pipe clamps and channel nuts. Also provided on rail systems are devices which are designed for hanging components and whose rod members can likewise be secured to the rail systems through the use of suitable fastening devices. Fastening devices having angle elements as contact plates, for example, are likewise used for connecting a plurality of rail elements.
For a rail system of this kind, what is generally referred to as a C-shaped mounting rail is often used, as is known, for example, from the German Utility Model Patent DE 87 15 256 U1. The interior space enclosed by the mounting rail is externally accessible via a mounting opening extending along the longitudinal extension of the mounting rail that is laterally delimited by rims. The mounting opening has a clearance width extending transversely to the longitudinal extension of the mounting rail that is smaller than the corresponding inside dimensions of the interior space of the mounting rail.
From the European Examined Patent Application EP 0 553 765 B1, a fastening device is known for clamping a conduit to a C-shaped mounting rail. The fastening device has a rear-engagement member which is configured to be introduced into the mounting opening and to engage behind the rims of the mounting opening of the mounting rail which has an internally threaded portion. The width of the rear-engagement member is smaller than the clearance width of the mounting opening, and its length is greater than the clearance width of the mounting opening. In addition, to clamp the fastening device to the mounting rail, the fastening device has a tensioning device in the form of a tensioning bolt which cooperates with the rear-engagement member and has a longitudinal axis, the tensioning bolt being connected by its inwardly threaded portion to the rear-engagement member. In addition, a contact plate having a feed-through opening for the shank of the tensioning bolt as part of the tensioning device, is provided for resting on the outside of the mounting rail. Configured between the contact plate and the rear-engagement member is a spring element for preloading the rear-engagement member circumferentially with respect to the longitudinal axis of the tensioning device. By way of a holding device between the rear-engagement member and the contact plate, the rear-engagement member is held in the preloaded position which corresponds to the insertion position of the rear-engagement member upon its introduction into the mounting opening of the mounting rail. The holding device encompasses recesses on the rear-engagement member that cooperate with projections on the contact plate. Upon introduction of the rear-engagement member into the mounting opening of the mounting rail, the holding device is released in the direction of the contact plate in response to axial displacement of the tensioning bolt; in response to the preloading exerted by the spring element, the rear-engagement member being moved from the insertion position to a rear-engagement position where it engages behind the rims of the mounting opening. The twisting rotation of the rear-engagement member is limited by stop faces provided thereon that come to rest against the mutually facing inner sides of the rims of the mounting opening.